Thermal conductivity of carboxymethyl cellulose-based Fe3O4 and Al2O3 nanofluids: An improved measurement method

In this study, the rheological coupling thermal conductivity (TC) measurement method was improved using two approaches. And this improved measurement was applied to study the thermal conductivities (TCs) of self-made carboxymethyl cellulose (CMC) based Fe₃O₄ and Al₂O₃ nanofluids (NFs). The results show that, the improved TC measurement method more accurately assesses the contribution of viscous dissipative heat (VDH) to TC, thereby significantly enhancing the precision of the measurement outcomes. For these two NFs, an interlinked effect is observed: an increase in either volume fraction or shear rate leads to a more pronounced enhancement of TC, with each factor amplifying the other’s influence. The maximum contribution of VDH to TC is 17.11% for Fe₃O₄ NF and 12.21% for Al₂O₃ NF, highlighting the significance of VDH in high-viscosity fluid flows. Based on the experimental data, a constitutive model for the TC dependence on shear rate and volume fraction was proposed. Rheological constitutive model of the two NFs is the Carreau model, and the parameters of the Carreau model are all quadratic polynomials of the nanoparticle volume fraction.